TABLE OF CONTENTS Introduction... pg. 2 Factors Creating the Demand For Secondary Storage... pg. 2 Why Buy Optical... pg. 3 CD Physical Characteristics... pg. 4 How Does a CD Work... pg 5 What is a CD-R... pg 5 What is CD-RW... pg 5 How Does A CD-RW Work... pg. 5 Advantages of CD-RW... pg. 5 DVD... pg 6 DVD vs. CD... pg 6 Glossary... pg 7 Questions... INTRODUCTION The use of optical storage continues to grow at an incredible pace. The word optical in the computer industry refers to any storage method which uses a laser to store and retrieve data from media. This term includes such devices as CD-ROM, re writable optical, WORM, CD-R, and optical jukeboxes or auto changers. Most of us are familiar with CD-ROM, but other terms such as re writable optical, WORM, and CD-R, may be foreign. Rewritable optical devices use media that allows data to be written repeatedly, while WORM technology writes data permanently to disk.
CD-R, stores information permanently to a compact disc and is read on low-cost CD-ROM drives. These devices are currently sold as single or standalone items. The continuing development of optical technology has opened up many new avenues and created limitless possibilities. Migration software now allows unused data to be moved from its original location to an optical device where it resides until it is needed.
Since the only thing that touches the media is the laser, it is the most durable way to store and archive data. Optical storage solutions are also used in a wide variety of applications such as document timing, records retention, backup systems, and desktop publishing. FACTORS CREATING THE DEMAND FOR SECONDARY STORAGE Because of its high capacity, low cost, durability, and random access to large amounts of networked information, secondary storage satisfies an essential need of data intensive organizations. This need for secondary storage arises from a number of factors: Digital convergence. The move towards graphical user interfaces and the success of operating systems, such as Windows, Windows 95, and Windows NT, have resulted in a significant increase in the average size of a stored document. Industry estimates indicate that the average document size has grown almost tenfold (PC Magazine, 03/10/98, 'To Write or Rewrite?' ) The information superhighway.
The explosive growth of on line services, led by the Internet, has resulted in unprecedented use of such services to reach potentially huge new customer base. Another consideration for the need of reliable secondary storage is the increasing cost of managing storage on network servers. According to Strategic Research Corporation, as storage requirements explode, organizations are finding that the cost of managing the storage is almost four times the cost of the actual storage due to server downtime, backup procedures, and hard disk failures. Low cost secondary storage alleviates many of these additional expenses because the data is permanent and easily portable in case of hardware failure (pr news: 9/9/99).
WHY BUY OPTICAL? Some may ask what does recordable CD technology have going for it, and why should you be interested? The answer is that CD's have two things that together make it a compelling choice for your removable storage needs. They include low cost per megabyte and near universal acceptance on Pcs.
The price of compact disk recordable drives and media have fallen to previously unimaginably low levels. You can find blank CD-R media for under $2 per disk. A little pricier than their CD-ROM counterparts (typically costing around $550), CD-R media (about $12 per disk), which, over time, can save you money. (See the table below from Disk Trend) CDs are also the only storage technology that is portable across hardware and platforms. Because of this standardization, a CD made on any operating system using any CD recorder can be accessed from any computer using any CD-ROM reader. The standard logical and physical interchange format of CD is especially important for companies wishing to archive information, since it minimizes technology risks from changes in operating systems and hardware in the future.
WORM and MO hardware and software are proprietary and, consequently, provide no flexibility or scalability to meet changing customer needs. Random Access is another advantage of CDs. Tape does not allow random access to any file. This means that data is sequentially retrieved, leading to delays of up to several minutes between data access. CDs, on the other hand, are randomly accessible, allowing access to any byte of data within 150 milliseconds. CD's random access makes it highly suited for large storage applications (PC magazine, 03/10/98, 'To Write or Rewrite?' ).
CD Physical Characteristics CDs are approximately 4.72 inches in diameter. The commercial producers of CDs are made of injection molded plastic formed from a stamper disc, painted with an aluminum coating and lacquered to protect the surface. The common specification agreed to by all CD-R media manufacturers and CD recorder manufactures is the Orange Book, Part II, which insures interoperability. The storage capacity of the CD-R and CD-R is 650 MB CD-R stands for compact disc-recordable. CD-R is often used to refer to write-once discs. The common specification agreed to by all CR-R media manufacturers and CD recorder manufactures is the Orange Book, Part II, which insures interoperability.
The estimated shelf life of CD-R media is estimated to be between 5 and 10 years (PC Upgrade and Maintenance Guide, 1999). The lifetime estimation of any storage medium is a very complex and statistics based process. The CD-R media manufacturers have performed extensive media longevity studies using these industry devine d test and mathematical modeling techniques, with results claiming longevity from 70 to over 200 years (Computer Technology Review 1/98). In other words, the media is as reliable as are your safeguards to insure proper handling and storage of the media.
CD SPEED The 'speed' rating of a CD-Recorder determines how fast it can record data to blank CD-R media. Speed designators, such as '1 x', 2 X', '4 X', '5 X', '8 X' define multiples of the original playback speed of first generation CD-ROM players. For a CD-ROM player or CD recorder a 1 X speed translates to 153,600 Bytes per second. This usually rounded down to 150 KB per second. Therefore, a '1 X' recorder writes 150 KB per second to the CD-R media. To view compact disc average transfer rates see the below table from Eastman Kodak Company.
HOW DOES A CD WORK? When you insert a CD into the drive the electronics inside sense the disc and a controller signals the spindle motor to begin spinning. The laser device is invoked and focus-control circuits adjust the optical beam to the size of the pits on the disc. The beams runs over the surface of the CD, reflecting light back to a which measures the reflected light and encodes it to a digital signal. This signal then transfers to the drive electronics, which gives it to the computer. (PC Upgrade and Maintenance Gud ie, 1999).
WHAT IS A CD-R? The CD-R is a compact disc that allows the user to create their own CDs. This is done by means of a recording system that uses 'write once' type optical discs standardized by Philips and Sony and documented in the 'Orange Book, Part II' and a CD recording device that is connected to a host system. Typically, the host system is a personal computer which also contains recording software. (PC Upgrade and Maintenance Guide, 1999). WHAT IS CD-RW CD-RW is the most recent addition to the compact disc family.
Originally tagged CD-Erasable, the official name is now CD-Rewritable. As the name implies, CD-RW is a media and recording system that allows the user to erase previously recorded information and then to record new information onto the same physical location on the disc (Computer Technology Review, 6/98). HOW DOES A CD-RW WORK? The rewrite is accomplished by means of a new CD-RW media using 'phase change' technology.
This allows a laser beam to change the media material from am orphic to crystalline by means of shift in recording power. The new CD-RW drives have all the functionality of previous CD-R drives, allowing them to write to CD-R media as well as adding the new function of erasing previously recorded information and recording new information on CD-RW media. The Orange Book, part defines CD-RW media in terms of physical characteristics and terms of playability and recording characteristics. Laser write strategies are defined, allowing CD-RW drive manufacturers to produce drives that can read this new CD media. ADVANTAGES OF CD-RW The introduction of CD-RW drives that can both read and write to CD-R media further strengthens the entire CD family. The user now has the choice of media to use for archiving and distribution applications versus backup and re- recording applications.
The drive costs and media costs will be different, further supporting the continuation of CD-R. DVDDigital Versatile Disc is co comprised of several models, each positioned to meet the needs of specific industries. DVD-Video and DVD-RAM and DVD-ROM, which were the first DVDs to hit the consumer market, are read-only versions that are ideal for full length feature films and computer games featuring highly advanced graphics. DVD-r and DVD-ram discs are designed to meet the ever increasing storage capacity demands of the computer industry, while DVD-audio will likely store entire compilations of musicians, whether it be 50 songs, 75 songs or more. DVD vs. CD The interesting thing about DVD descriptions is that they sound a lot like CD products except there are some important liked differences between the two, the first being storage capacity. DVD discs make CDs look like the 5 1/4' floppy disks of earlier times. Just the single sided, single layer DVD disc itself offers 4.7 GB of capacity, which is world's away from a CDs 680 MB capacity.
What makes DVD superior to its CD counterpart is the manufacturing process and internal design. The basic manufacturing process for DVD is similar to the current process for cd-rom, with some exceptions. Two injection molders are required to make one DVD, which consists of two bounded. 6 mm discs. The second additional manufacturing step is hot-melt glue bonding or UV bonding. For the dual layer design, a semi-reflective layer is also added to allow both information layers to be read from one side of the disc.
DVD also uses a high resolution laser beam to write a glass master in addition incorporating a new semi-reflective layer rather than the standard aluminum layer in CD-ROM. This internal design provides DVD with the major advantage over CD. Another interesting feature of DVD is that the discs's second data layer can be read from the inside of the disc out, as well as from the outside in. In standard-density CDs, the information is always stored first near the hub of the disc.
The same will be true for single and dual-layer DVD, but the second layer of each disc can contain data recorded 'backwards,' or in a reverse spiral track. With this feature, it takes only an instant to refocus a lens from one reflective layer to another. On the other hand, a single-layer CD that stores all data in a single spiral track takes longer to relocate the optical pickup to another location or file on the same surface. DVD-R will provide 3.9 GB and DVD RAM featuring 2.6 GB and 5.2 GB these discs will have enough capacity to meet a variety of storage application needs. Besides being able to backup almost anything or download graphic intensive INTERNET items, end users will be able to develop, run interactive multimedia presentations and / or programs with animated cartoons and other interesting video-based components (cd-info. com).
CONCLUSION Optical Storage technology offers speedier and higher quality access to records than current access to records preserved in microfilm, microfiche or physical format. Optical disk storage of a company's records will increase productivity and ensure security. CD-R and CD-RW and DVD are optical storage devices that offer new and exciting storage capacities and data recording possibilities. One thing is for sure the 21st century, technology will be developed into things that were once unimaginable.
GLOSSARY A Time (or absolute time) In an audio CD, the time elapsed since the beginning of the disc. It can be used in determining the start and stop times of sound segments for programming an application on a mixed mode disc, measuring from the very beginning of the data area (including the computer data in Track 1). CD Compact Disc, a digital medium formed of a 12 cm polycarbonate substrate, a reflective metalized layer, and a protective lacquer coating. The physical format of CDs is described by the ISO 9660 industry standard. CD Recordable discs also have an organic dye data layer between the substrate and the metal reflective layer. CD Compact disc recordable.
When referring to recordable discs (media),' CD R' is often used to refer to write once discs, in contrast to CD RW. CD ROM Compact Disc Read Only Memory. A standard for compact disc to be used as digital memory media for personal computers. The specifications for CD ROM were first defined in the Yellow Book.
CD ROM Drives peripheral device attached to a computer which allows it to read / play aCD ROM disc. All CD ROM players can also play back audio CDs, but you need external headphones or speakers to hear the mCD RW CD ReWritable. CD recordable media which can be erased andre recorded. CD RW media can only be written in a CD RW recorder, not in a normal CD recorder, though a CD RW recorder can also record standard CD R discs. More information on the read back compatibility of CD RW discs.
DVDDigital Video Disk (DVD) is a method of getting more data onto a single disc by compressing it. DVD can store about 4 GB of information. Multisession A method of adding data incrementally to a CD in more than one recording session. If data is linked between session, all data on disc, when read on a multi session CD ROM drive, may be seen as part of a single logical structure. Multisession is very different from packet writing. For more information.
Orange Book The Orange Book is the specification for CD Recordable. pits & lands - In a 'pressed' or mass replicated CD, the bumps and grooves that represent the binary data on a disc. Sector The smallest recordable unit on a CD. A disc can contain [ (75 sectors per second) x (60 seconds per minute) x (number of minutes on disc) ] sectors. The amount of data contained in the sector depends on what physical format it is recorded in; for 'regular' CD ROM data, you can fit 2048 bytes (2 kilobytes) of data into a sector.
Track at Once A method of writing data to disc. Each time a track (data or audio) is completed, the recording laser is stopped, even if another track will be written immediately afterwards. Link and run blocks are written when the laser is turned on and off. QUESTIONS 1.
What Book is the specification for CD-Recordable. Red Book. Blue Book. Orange Book.
Black Book 2. Which of the following is not a reason for an increase in demand for secondary storage a. high capacity. durability c. flexibility d. low cost 3. WORM Means. Write once read multiples b. Write once rewrite many. Write once read many.
Write once record many 4. The speed rating of a CD- Recorder determines: a. how fast it can locate information. how fast it can load data. how fast it can record data to blank CD-R media. how fast it can print information 5. DVD stands fora. Digital Versatile Disc. Digital Variable Disc. Digital Vital Disc.
Disc Variable Digit 6. What is the smallest recordable unit on a CDa. track. cylinder c. sector d. byte 7. What is a method of adding data incrementally to a CDa. Multisession.
Multitrackingc. Synchronous Additions. Random Additions 8. DVD can store about how much information a. 8 MBb. 720 KBc.
4 Gb. 32 MB 9. The CD-RW works by using what type of technology a. Rewritable tracks. phase change. Polym or writing. Interchangeable sectors 10.
DVD gets more information onto a single disc by: a. storing the information onto Ram. storing the information onto Rom. compressing the information. moving the information into hidden sectors.